[PATCH v2 0/4] STIG Mode Fixes for spi-cadence-qspi driver

[Dhruva Gole]

* Reset the CMD_CTRL Register, without which read/writes in STIG mode
were failing in some cases. The issue came to light while using STIG
Mode for small reads.
* Also add a flag that can allow us to do direct reads but distinguish
direct writes, thus enabling us to disable writes in DAC mode in some
cases that require it. (Like to write to some connected Flash registers)
* Fix register reads in STIG mode and also use STIG mode while reading flash
registers.
Currently if you try to read a register while in STIG mode there is no
support for ADDR and thus naturally a register never gets read from the
flash.

This patch series has been tested on a TI AM625-SK-EVM with both a quad
spi nor flash (s25hs) and OSPI NOR Flash (s28hs).

Output of ltp-ddt test, "DD_RW_ERASESIZE_UBIFS" run with s25hs512t flash:
...
[    2.334068] spi-nor spi0.0: s25hs512t (65536 Kbytes)
[    2.339185] 7 fixed-partitions partitions found on MTD device
fc40000.spi.0
[    2.346158] Creating 7 MTD partitions on "fc40000.spi.0":
[    2.351555] 0x000000000000-0x000000080000 : "ospi.tiboot3"
[    2.358344] 0x000000080000-0x000000280000 : "ospi.tispl"
[    2.364788] 0x000000280000-0x000000680000 : "ospi.u-boot"
[    2.371311] 0x000000680000-0x0000006c0000 : "ospi.env"
[    2.377519] 0x0000006c0000-0x000000700000 : "ospi.env.backup"
[    2.384419] 0x000000800000-0x000003fc0000 : "ospi.rootfs"
[    2.390890] 0x000003fc0000-0x000004000000 : "ospi.phypattern"
..snip..
Test Start Time: Wed Jan 11 21:14:31 2023
-----------------------------------------
Testcase                                           Result     Exit Value
--------                                           ------     ----------
OSPI_S_FUNC_DD_RW_ERASESIZE_UBIFS                  PASS       0

-----------------------------------------------
Total Tests: 1
Total Skipped Tests: 0
Total Failures: 0
Kernel Version: 6.2.0-rc1-00040-g700d796a94e0-dirty
Machine Architecture: aarch64
Hostname: am62xx-evm
...

Previous version link:
https://lore.kernel.org/linux-spi/20230104062604.1556763-1-d-gole@ti.com/

Changelog:

* This version addresses concerns from Vaishnav where he was seeing issues
while testing on different platforms.
* Also has additional patches that fix the issues that came to light
while using STIG Mode.

To: Mark Brown <broonie at kernel.org>
Cc: Vaishnav Achath <vaishnav.a at ti.com>
Cc: Pratyush Yadav <pratyush at kernel.org>
Cc: Vignesh Raghavendra <vigneshr at ti.com>

Dhruva Gole (4):
  spi: cadence-quadspi: Reset CMD_CTRL Reg on cmd r/w completion
  spi: cadence-quadspi: Add flag for direct mode writes
  spi: cadence-quadspi: setup ADDR Bits in cmd reads
  spi: cadence-quadspi: use STIG mode for small reads

 drivers/spi/spi-cadence-quadspi.c | 42 ++++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 4 deletions(-)

--
2.25.1